Xie et al. recently described ‘a reverse genetic system that enables rapid synthesis of wild-type, mutant and reporter SARS-CoV-2 [severe acute respiratory syndrome coronavirus 2] strains’1. Their goal was to enable researchers to assess the functional properties of sequence variants, including their susceptibility to countermeasures such as vaccine-induced immune responses. We agree that the rapid development of medical countermeasures is of utmost importance, especially during an ongoing pandemic. However, we believe that public dissemination of this protocol in its current form poses risks that outweigh the benefits. In providing detailed, step-by-step instructions, it enables anyone skilled in the art anywhere in the world to create novel variants of SARS-CoV-2 more quickly, including variants that have even more worrisome properties than those that have occurred naturally. Sometimes research should be slowed, not hastened, to ensure a proper discussion of goals and a full and public vetting of proposed plans. Detailed protocols pose special risks under certain circumstances like this one and should undergo special prepublication scrutiny.